Russian propaganda:
"Since 2014, the Ukrainian army has been killing children of Donbass..."
You can read all about this in western media. You weren't aware of it?
https://www.dw.com/en/ukraine-the-forgotten-victims-of-donbass/a-42597692
https://www.thecitizen.co.tz/tanzania/news/international/how-many-lives-has-the-war-in-donbass-taken--3724098
https://www.prnewswire.com/news-releases/luca-belardi-releases-a-documentary-about-the-children-of-the-war-torn-donbass-region-301433264.html
Around 3.5k civilians killed. https://en.wikipedia.org/wiki/War_in_Donbas_(2014%E2%80%932022)#Casualties
You think wikipedia is Russian propaganda?
None of those articles frame Ukraine as child killers, except the article from Tanzania(!) and that tweet or now X(?) in the OP.